The invention relates to a technology effective for application to a high frequency power amplifier circuit used in a wireless communication system, such as a cellular phone, and so forth, for amplifying a high frequency transmitting signal to be subsequently outputted, and electronic components with the same mounted therein, and more particularly, to a technology effective for application to an output power detection circuit for executing detection of an output level, necessary for feedback control of an output power.
In general, a high frequency power amplifier circuit for amplifying modulated signals is assembled in an output unit on the sending side of a wireless communication equipment (mobile communication equipment) such as a cellular telephone, and so forth, and with the conventional wireless communication equipment, it has been in practice to detect an output level of a high frequency power amplifier circuit or an antenna to implement feedback of the output level in order to control an amplification factor of the high frequency power amplifier circuit, according to a transmission level required by a baseband circuit or a control circuit of a microprocessor, and so forth (refer to, for example, Patent Document 1). In the past, the detection of the output level has generally been implemented by use of a coupler, a diode detection circuit, and so forth, and a detection circuit has been often made up as a semiconductor integrated circuit separate from the high frequency power amplifier circuit. Since an output power detection system for the conventional high frequency power amplifier circuit makes use of a large number of the semiconductor integrated circuits separate from the high frequency power amplifier circuit, and electronic components, it has been difficult to implement miniaturization of a module.
Further, in the case of a late model cellular telephone, there has been proposed a cellular telephone of a dual-band system capable of handling signals of a system such as DCS (digital Cellular System) using frequencies in, for example, a 1710 to 1785 MHz band besides a system called GSM (Global System for Mobile Communications) for using frequencies in a 880 to 915 MHz band while shifting the phase of a carrier wave by a phase modulation system called GMSK (Gaussian Minimum Shift Keying that shifts the phase of the carrier wave according to transmission data. With a high frequency power amplifier circuit for use in such a cellular telephone as described, since output power amplifiers corresponding to respective bands are provided, there is the need for couplers, and diode detection circuits amplifiers for detecting the respective output levels of the output power amplifiers, corresponding to the respective bands, so that it becomes more difficult to implement miniaturization of the module.
Under the circumstances, the applicant for the present invention has developed the invention relating to a wireless communication system of a current detection scheme, comprising an output detection transistor for receiving an input signal of a power amplification transistor for amplifying a high frequency transmitting signal, and causing a current proportional to a current flowing in the power amplification transistor to flow therein, and a current mirror circuit for transferring the current of the output detection transistor, wherein a current flowing in a receiver of the current of the current mirror circuit is converted into a voltage to serve as a detection signal of an output level, and an output control voltage Vapc corresponding to an input potential difference is generated by comparing the detection signal with an output level directive signal delivered from a baseband circuit, thereby controlling a bias of the power amplification transistor, whereupon the applicant has submitted an application for the same (Patent Document 2).
(Patent Document 1)
    JP-A No. 151310/2000.(Patent Document 2)    International Publication No. WO 2004/023469